Sen Ananya, Hou Gao-Lei, Wang Xue-Bin, Dessent Caroline E H
Department of Chemistry, University of York , Heslington, York YO10 5DD, U.K.
Physical Sciences Division, Pacific Northwest National Laboratory , MS K8-88, P.O. Box 999, Richland, Washington 99352, United States.
J Phys Chem B. 2015 Sep 3;119(35):11626-31. doi: 10.1021/acs.jpcb.5b07108. Epub 2015 Aug 14.
We report the first low-temperature photoelectron spectra of isolated gas-phase complexes of the platinum II cyanide dianion bound to nucleobases. These systems are models for understanding platinum-complex photodynamic therapies, and a knowledge of the intrinsic photodetachment properties is crucial for characterizing their broader photophysical properties. Well-resolved, distinct peaks are observed in the spectra, consistent with complexes where the Pt(CN)4(2-) moiety is largely intact. Adiabatic electron detachment energies for the dianion-nucleobase complexes are measured to be 2.39-2.46 eV. The magnitudes of the repulsive Coulomb barriers of the complexes are estimated to be between 1.9 and 2.1 eV, values that are lower than for the bare Pt(CN)4(2-) dianion as a result of charge solvation by the nucleobases. In addition to the resolved spectral features, broad featureless bands indicative of delayed electron detachment are observed in the 193 nm photoelectron spectra of the four dianion-nucleobase complexes and also in the 266 nm spectra of the Pt(CN)4(2-)·thymine and Pt(CN)4(2-)·adenine complexes. The selective excitation of these features in the 266 nm spectra is attributed to one-photon excitation of [Pt(CN)4(2-)·thymine]* and [Pt(CN)4(2-)·adenine]* long-lived excited states that can effectively couple to the electron detachment continuum, producing strong electron detachment signals. We attribute the delayed electron detachment bands observed here for Pt(CN)4(2-)·thymine and Pt(CN)4(2-)·adenine but not for Pt(CN)4(2-)·uracil and Pt(CN)4(2-)·cytosine to fundamental differences in the individual nucleobase photophysics following 266 nm excitation. This indicates that the Pt(CN)4(2-) dianion in the clusters can be viewed as a "dynamic tag" which has the propensity to emit electrons when the attached nucleobase displays a long-lived excited state.
我们报道了与核碱基结合的孤立气相二价铂氰化物络合物的首个低温光电子能谱。这些体系是理解铂络合物光动力疗法的模型，了解其本征光致脱附特性对于表征其更广泛的光物理性质至关重要。在光谱中观察到分辨率良好、清晰的峰，这与其中Pt(CN)4(2-)部分基本保持完整的络合物一致。二价阴离子 - 核碱基络合物的绝热电子脱附能测量值为2.39 - 2.46电子伏特。由于核碱基对电荷的溶剂化作用，这些络合物的排斥库仑势垒大小估计在1.9至2.1电子伏特之间，该值低于裸Pt(CN)4(2-)二价阴离子的势垒值。除了分辨出的光谱特征外，在四种二价阴离子 - 核碱基络合物的193纳米光电子能谱以及Pt(CN)4(2-)·胸腺嘧啶和Pt(CN)4(2-)·腺嘌呤络合物的266纳米光谱中还观察到了指示延迟电子脱附的宽无特征带。在266纳米光谱中对这些特征的选择性激发归因于[Pt(CN)4(2-)·胸腺嘧啶]*和[Pt(CN)4(2-)·腺嘌呤]*长寿命激发态的单光子激发，这些激发态可以有效地耦合到电子脱附连续体，产生强烈的电子脱附信号。我们将此处观察到的Pt(CN)4(2-)·胸腺嘧啶和Pt(CN)4(2-)·腺嘌呤的延迟电子脱附带归因于266纳米激发后各个核碱基光物理的根本差异，而Pt(CN)4(2-)·尿嘧啶和Pt(CN)4(2-)·胞嘧啶则没有这种现象。这表明簇中的Pt(CN)4(2-)二价阴离子可以被视为一个“动态标签”，当附着的核碱基显示出长寿命激发态时，它有发射电子的倾向。
